1988 150 mercury2.0 wont turn over 5000 rpms

[BJ guidry]

How you guys doing. This is my first post and Im here looking for some answers and anything is appreciated. Im running out of ideas.

So anyway, what I have is a 150 merc 2.0 that I cant get to turn more than 5000 rpms. The motor is on a 5 ft wide 19ft long aluminum flat bottom boat. I am turning a 14.25x17 prop and the motor will not trun up. With that size boat i would think it would be way higher. I have had 3 other props, Checked carbs/jetting, checked coils, linkage's, tried a 1.87:1 gear ratio and a 2:1 gear ratio LU, new plugs and it as good compression. the motor sound s good/smooth, dosent miss,spit or sputter. No matter what all it will turn up is 5 grand and no more. I also think its burning more fuel that it should.

So can anyone help me. Thanks guys.

 

[sschefer]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

The key is probably that it's running rich. I don't know if you have the advance module on it still but if you can get to 5 that's probably not it.

If it's running rich, it's running cold. Heat = pressure and the lack of heat is the likely culprit. Try running wide open for a few minutes then shut it off and pull a plug or two and see what they look like. They should be a coffee tan color. If they're wet or black your running too rich. Check your timing first then look into the high speed jetting.

One caution, you're walking a fine line with todays fuels and yesterday's jetting so be carefull not to make any major changes. After any change. thoroughly check the results at the plugs and the piston tops. The piston top on a race motor would be light tan but on a fishing motor you want them fairly dark or they won't last long.

 

[j_martin]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

If advance module were disconnected or inop, and the base timing was still 19 degrees, that'd do it.

I'd discard the advance module and do a link n sync by the book except max advance at 23 degrees.

Could be as simple as slow timing, or throttle plates not fully opening.

hope it helps
john

 

[BJ guidry]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

It aint the throttle plates i know that for sure. What Is a link in sync?

 

[j_martin]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

It aint the throttle plates i know that for sure. What Is a link in sync?

It's the official linkage and timing adjustments procedure. It's in the Mercury maintenance manual for your engine. If you don't have one, get it.

What does it do when it gets to 5000 rpm. Does it 4 cycle, stumble, balk and back off, or just crawl up to 5 grand? Are you sure you're running on all 6?

 

[BJ guidry]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

It hits 5 grand and bounces betweent 4800 and 5000. If it isnt hittin on all six I cant hear it or feel it. The rest of the way through the throttle it feels good. But is seems to be burning alot of fuel.

 

[j_martin]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

It hits 5 grand and bounces betweent 4800 and 5000. If it isnt hittin on all six I cant hear it or feel it. The rest of the way through the throttle it feels good. But is seems to be burning alot of fuel.

I'd be willing to bet you're dropping a cylinder or 2. If it were mine, the next thing I'd do is look at plugs and cylinders to see if one is starving, misfiring, or maybe getting water in it. You don't want to blow it up trying to shoot an electrical bug when it's a fuel or gasket problem.

If all looks reasonable, next would be to check for spark when it's faulting. Easiest done with an induction timing light, clamped on each plug wire in turn, then take a run and see if it fires the light.

hope it helps
John

 

[BJ guidry]

Re: 1988 150 mercury2.0 wont turn over 5000 rpms

Itwas a power pack. Put a new one on to replace the rear pack and now she turns 6500 with that 17p prop. Gotta go get a new prop now. Thanks for the help.